CurtPalme.com Home Theater Forum

[benny]

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I'm hoping some more knowledgeable folks here can provide guidance to fix an issue a mate has with his 909.

In the middle of a movie, the green gun was suddenly overdriven, to the extent that the whole image was awash with green and you can see the occasional retrace lines clearly.

No unusual symptoms leading up to the issue.

Have looked back through numerous 909 related threads, but if it was discussed, my search results didn't list it.

My mate normally runs his PC that feeds the 909 at 1920x1080@59.94Hz.

We eliminated the source and leads as the culprit by switching the green and red BNC leads, but same issue with overdriven green gun.

Turning down the BRI or CON makes no difference other than the expected result from those functions.

Turning down the BIAS and GAIN in the colour balance controls didn't fix issue.

Interestingly, when we fed the 909 with progressively lower res's, the overdriving was slowly reduced, with the result that a 640x480 input had the green gun almost back to normal.

Internal test patterns worked fine provided another unused input port was selected. (I think I'm right with that. Memory a little hazy now as we tried all manner of ideas).

No recent errors listed in the log menu.

I have a number of supposedly working spare cards to try, but hoping some insight as to the cause is out there to narrow down the replacement swaps. My limited understanding on 909 internals suggests it may be related to input signal handling, but that's a complex operation.

Thanks in advance,

Russ

[cmjohnson]

Swap neck cards between green and one other tube. If the problem follows the neck card, it's the neck card.

If not, it's obviously not the neck card.

Process of elimination by substitution.

What's happening appears to be that your G2 voltage is dropping. The higher the G2 voltage, the dimmer the image. Losing G2 voltage makes the tube go to full output.

[Curt Palme]

Most likely the green neck board. THe main chip, which is unobtanium, has failed. Swap the green CRT card with the red (don't switch it to the blue). All three are identical, and are easy swaps. I've got spares if you don't have one.

[Curt Palme]

Most likely the green neck board. THe main chip, which is unobtanium, has failed. Swap the green CRT card with the red (don't switch it to the blue). All three are identical, and are easy swaps. I've got spares if you don't have one.

[benny]